The present invention relates to apparatus for the connection of pipe liners. In particular, the apparatus provides a connector suitable for use with a liner employed in a vented oil, gas or other service pipeline.
It is known to those skilled in the art that pipelines and other fluid transport systems (such as tubing used down-hole in oil wells and process pipework in refineries and the like) can have their lifetimes significantly increased by employing a liner. The liner is incorporated within the pipeline so as to reduce the detrimental effects of corrosion or erosion by isolating the bulk fluid from the pipe wall, however they are not intended to be completely impermeable to gases.
The primary restriction on the use of such liners is liner collapse due to pressure build up of gases in the micro-annulus between the liner and the parent pipe. If the differential pressure between the micro-annulus and the pipe bore become sufficient, the liner may collapse and suffer damage.
In PCT Application WO 02/33298 the authors themselves teach of a vented liner that permits controlled communication between the micro-annulus and the bore of the pipe so as to permit pressure balancing and consequent limitation on the pressure differential and the tendency for collapse. However, with any such lined pipe, specific consideration must be given to the physical engineering and construction processes employed to form complete lined fluid transport or pipework system, and this gives rise to a number of ways in which a liner may be inserted.
In some cases it is desirable to pass a length of liner through a significant number of joined pipe sections, whilst in other cases it is desirable to join individual sections of lined pipe. Whichever method is employed, the liner must be terminated at some point, and some means of maintaining the continuity of the corrosion barrier across the joint must be found. This is a particular challenge where the method of jointing is to employ heat (such as welding) as the liner may be degraded during the process. As a result, the liner is often terminated short of the joint so that it will be unaffected by the heat generated during joining. It can also be desirable to terminate the liner short of the joint so as to permit the entry of tools and handling aids into the ends of the pipes without causing damage to the liner in the vicinity of the joint, or affecting the operational effectiveness of the tools employed.
As with any such pipeline specific consideration must be given to the physical engineering and installation of the pipeline with actual operational conditions. It is often problematic to pass a length of liner through a significant number of pipe sections. Therefore it makes practical sense to have a liner section associated with each pipe section, the liner being connected together when the pipe sections are welded.
U.S. Pat. No. 5,992,897 (British Gas/Tom Hill et Al., known as ‘Weldlink’) teaches of one method of terminating a liner that relies on a layer of corrosion resistant metal to continue the corrosion resistance of the lined system across the joint. However, this method has been found to be very expensive because it relies on high-cost corrosion resistant metallic components and time-consuming work methods.
U.S. Pat. No. 3,508,766 (AMF Tuboscope/Kessler et Al.) teaches of a cylindrical corrosion barrier that contains a heat resistant material that allows welding to be used to join sections of pipe lined with materials that would otherwise be degraded on exposure to high temperatures. To minimise the impact on the bore of the pipe caused by the insertion of the cylindrical barrier, this patent envisages the pipes being formed with belled ends. The cost of providing the belled ends has been found to be prohibitive.
U.S. Pat. No. 4,913,465 (Tuboscope/Abbema et Al., known as ‘Thru-kote’) also teaches of a cylindrical corrosion barrier for connecting lined pipe sections where welding is to be performed, but in this patent, the cylindrical barrier is entirely within the bore of the host pipe. This method is also unsatisfactory to high-pressure applications because the cylindrical corrosion barriers contain voids of air and other compressible material between the face exposed to pressure and the wall of the host pipe. The leak-tight seals at either side of the joint cause a differential pressure between these voids and the bore of the pipe giving rise to considerable expansion forces which cause it to deform uncontrollably, causing damage and distortion. Increasing the thickness of the cylinder may resist this, but for high pressure applications, this imposes an unacceptable restriction on the bore of the pipe.
A further unsuitable aspect of sealed methods of bridging the joint in a liner occurs where gases may permeate or otherwise accumulate into the sealed spaces and voids between the cylindrical insert and the host pipe. In such circumstances when the pipeline pressure is reduced, collapse may result in the same way as described in the authors own PCT Application WO 02/33298 for the liner itself.